1. Field of the Invention
The present invention relates to an accumulator having a bellows, which is used for pressure accumulation or pulsation absorbing in hydraulic devices in automobile brake systems and various industrial hydraulic systems. The present invention further relates to a manufacturing process for accumulators such as the above, and more specifically relates to a joining method for shells which form a vessel for enclosing oil and gas therein.
2. Background Art
FIG. 5 shows an accumulator used for hydraulic devices in automobile brake systems and various industrial hydraulic systems. The inside of a housing 31 acts as a pressure vessel and is partitioned into a gas chamber 33 in which a compressed gas is sealed therein and a hydraulic chamber 34 by a metallic bellows assembly 32. The metallic bellows assembly 32 comprises an elastic metallic bellows 35, of which one end is fixed to the housing 31 and the free end thereof is equipped with a valve 37. The hydraulic chamber 34 defined in the interior of the housing 31 and exterior of the metallic bellows 35 is communicated with an external system through an opening 38a provided in the housing 31 and a flow path 38.
In such accumulator, when the hydraulic pressure transmitted from the flow path 38 is lower than the gas pressure sealed in the gas chamber 33 and the pressure in the hydraulic chamber 34 coincides with the low pressure, a differential pressure occurs between the gas chamber 33 and the hydraulic chamber 34. As a result, the metallic bellows 35 is extended and the valve 37 is thrust and closely contacted to the circumference of the opening 38a, thereby closing the opening 38a, and the valve 37 therefore self-seals so as to make the pressure of the hydraulic chamber 34 greater that of the gas chamber 33.
The valve 37 may not be able to exhibit sealing properties in closing due to factors such as aging degradation thereof and jamming of foreign matter such as dust. When the pressure transmitted from the flow path 38 is low, the pressure in the hydraulic chamber 34 also becomes low. As a result, stress is generated in the metallic bellows 35 due to the differential pressure between the hydraulic chamber 34 and the gas chamber 33, so that the durability thereof is lowered.
The end plate of the accumulator must be thick since it is slab-shaped, which results in increased weight of the overall accumulator. Therefore, end plates having semicircular or semi-ellipsoid cross section, which can disperse stress, are mainly used.
In accumulators, the stroke of the metallic bellows contained therein is essential for designing the volume of the gas to be sealed therein. The cylindrical portion of the pressure vessel is effective for pressure accumulation. In the end plates having semicircular or semi-ellipsoid cross section, the curved portion is a dead space and is generally employed merely for containing the liquid. Therefore, it has been desired to effectively use this dead space.
The accumulator absorbs pulsation by the elastic motion of the metallic bellows. However, the pressure of the pulsation occurring at a pressure lower than that of the sealed gas is lower than the operating pressure of the accumulator, so that the pulsation cannot be absorbed by the above construction. Heretofore, a special resonance box having a frequency corresponding to the pulsation is provided to absorb the pulsation. This results in large design and increased weight of the accumulator.
The pressure vessel of the accumulator consists of at least two shells for containing the bellows and other necessary parts, and such a manufacturing process is applied so that the bellows and the like are attached to one shell, and another shell is then put over the bellows and the like and is joined to the other shell. In the conventional joining method, the outer surface portion of the joining portion has been welded over the entire circumference by gas welding or tungsten inert gas welding.
However, these welding methods require long operation time, and mass-production efficiency is therefore not good and production cost is relatively high. Therefore, developments in methods for efficiently joining shells have been desired.